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Effects of platelet antagonists on the reduction in platelet density caused by microbubbles in vitro
Abstract:
Platelet-rich plasma (PRP) was stirred and incubated at 37 degrees C with N2 microbubbles in vitro in the presence and absence of platelet antagonists. The N2 microbubbles acted as a platelet agonist, like "classical" agonists such as ADP, collagen, and thrombin, causing an agonist-induced aggregation requiring extracellular Ca2+. This aggregation is abolished by 2-ethylamineglycolether (N',N',N',N') tetraacetate (chelator of extracellular Ca2+), and 2-deoxy-D-glucose plus antimycin A (inhibitors of glycolysis and electron transport, and thereby of ATP production). Furthermore, this aggregation could be depressed pharmacologically by several antagonists of the aggregation induced by "classical" platelet agonists. The greatest inhibition of microbubble-induced aggregation was obtained by substances that increase the intracellular levels of cyclic AMP. Medications that are in common clinical use, such as theophylline, seem promising in this respect. The prostaglandin-thromboxane pathway did not seem to be involved in the N2 microbubble-induced platelet aggregation in vitro, since acetylsalicylic acid and indomethacin were without effect, nor did the 3',5'-cyclic guanosine monophosphate pathway seem to be linked to this aggregation mechanism.
Insights
Nitrogen (N2) microbubbles activate platelets, causing aggregation similar to traditional agonists. This process requires calcium and ATP, and can be inhibited by drugs that increase cyclic AMP levels.
Area of Science:
- Biomedical Engineering
- Hematology
- Pharmacology
Background:
- Platelet-rich plasma (PRP) is a concentrate of platelet growth factors.
- Microbubbles are used in medical imaging and therapy.
- Platelet activation is crucial for hemostasis and thrombosis.
Purpose of the Study:
- To investigate the mechanism of platelet aggregation induced by nitrogen (N2) microbubbles.
- To compare N2 microbubble-induced platelet activation with classical platelet agonists.
- To identify potential pharmacological interventions to modulate microbubble-induced platelet aggregation.
Main Methods:
- In vitro incubation of PRP with N2 microbubbles at 37°C.
- Assessment of platelet aggregation in the presence and absence of platelet antagonists and inhibitors.
- Pharmacological evaluation using various inhibitors, including calcium chelators, metabolic inhibitors, and cyclic AMP-elevating agents.
Main Results:
- N2 microbubbles act as platelet agonists, inducing aggregation that requires extracellular calcium (Ca2+) and ATP.
- Aggregation was inhibited by ethylenediaminetetraacetic acid (EDTA), 2-deoxy-D-glucose, and antimycin A.
- Pharmacological agents, particularly those increasing intracellular cyclic AMP (e.g., theophylline), significantly inhibited microbubble-induced aggregation.
- The prostaglandin-thromboxane and cyclic guanosine monophosphate pathways were not involved.
Conclusions:
- N2 microbubbles induce platelet aggregation through a Ca2+-dependent pathway requiring ATP.
- Theophylline and similar agents show potential for controlling microbubble-induced platelet aggregation.
- Understanding this mechanism is vital for safe application of microbubble-based technologies.